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                <h2 class="heading-v1-title">当你按下电源键之后，计算机是如何启动的？</h2>
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                   <h3 style="color: blue;">
	<span style="color:#000000;"><span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">一个程序是如何开始运行的呢？这个问题，一千个人有一千种回答。电脑用户说：&ldquo;双击程序图标就行了啊。&rdquo;；初级程序员信心满满的回答：&ldquo;是从main函数开始执行的。&rdquo;；高级程序员也许会和你聊到c运行时库，那里才是程序编译运行的第一条指令；而熟悉操作系统的专家却并不知道如何说起，程序加载器、重定位、堆和栈的建立、进程和线程的创建等等细节闪过脑海，哪里才是真正的源头呢？</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">同样问道计算机是如何启动的，也许答案就是按下电源键而已。但在那个简单到极致的动作后面却隐藏了复杂的机理。启动的开始并不仅仅是操作系统引导，亦或BIOS运行，甚至CPU在reset vector执行第一条指令之前，很多事情已经发生了。正如地球生命的发端并不由人类的到来而伊始，秘密隐藏在远古而不为人知的远古时代。让我们顺着时间回溯，站在一切发生的起点：&ldquo;电源键按下&rdquo;，通过时间的流转，梳理其中所有的硬件软件过程，来深入了解计算机的工作原理。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">史前时代：上电时序<br />
	<img alt="" src="/uploads/171127/1-1G12H14452321.jpg" style="width: 640px; height: 391px;" /></span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">上电时序，也叫做Power-up Sequence，是指电源时序关系。它牵扯到诸多计算机部件，在正式开始时间之旅之前，我们来介绍一下所有参与的小伙伴们。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">电源</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">ATX电源提供+12V、-12V、+5V、-5V、+3V和+5VSB等六种电压。也就是我们图上的两个白色的电源接入口。主板其他的不同电压是主板上的变压线路转换过来的，他们包括+3VSB、+1.5VSB、1.8VDual、2.5VDual、3VDual、VCore、VTDDR等等很多。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">+12V主要是给CPU内核供电，它可以单独给PCIe设备供电，包括显卡等等。+5V应用最广，给USB等等外设供电。+5VSB等各种带SB的电压，是提供Stand By的供电，即在S3 Sleep时提供电力，保障唤醒和刷新。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">主板右边中间那个纽扣电池，它叫做RTC电源，永不掉电。除非电池没电并且没接任何外部电源。 RTC用以保持机器内部时钟的运转和保证CMOS配置信息在断电的情况下不丢失。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">时钟<br />
	<img alt="" src="/uploads/171127/1-1G12H1452U05.jpg" style="width: 606px; height: 385px;" /></span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">电脑中的CPU，AGP、PCI插槽、SATA、USB端口和PS/2端口等在通信速度上有很大差异，所以需要提供不同的时钟频率。由ck410、ck505和iCLK等芯片将原先散布在不同地方的晶振和分频电路整合在一起，为CPU、SATA、PCI、USB等等设备提供基础频率。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">电源时序控制芯片/电路</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">主板对于上电的要求是很严格的，各种上电的必备 条件都要有着先后的顺序，一项条件满足后才可以转到下一步，如果其中的某一个环节出现了故障，则整个上电过程不能继续下去。谁来控制和协调整个时序过程呢？不同的主板、芯片组、代际之间都有不同的方案，在笔记本上过去经常采用EC的方案、台式机则很多用SIO或者定制芯片。现在很多电源时序控制被整合进了ME中，在面向嵌入式设备的Atom系列主板上则越来越多的引入了在手机等设备上常用的PMIC。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">时间开始<br />
	<img alt="" src="/uploads/171127/1-1G12H14554515.jpg" style="width: 640px; height: 339px;" /></span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">我们通过一个古老的例子来了解一下开机的整个过程：</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">在G3（未接电源）情况下，RTC电源提供RTC_RST#和VCC_RTC电源给南桥。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">插入电源或者电池。系统进入G2，S5的状态。EC检查电源的可靠性，并发送PM_RSMRST#通知南桥各种SB电压已经准备完毕。南桥复位，部分功能SB功能激活，进入待机状态。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">用户按下电源键，时间开始。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">EC收到PWRSW</span></span><span style="margin: 0px; padding: 0px; text-decoration-line: none; cursor: pointer; font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;"><span style="color:#000000;">#信号，通过PM_PWRBTN#</span></span><span style="color:#000000;"><span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">通知南桥。南桥收到PM_PWRBTN</span></span><span style="margin: 0px; padding: 0px; text-decoration-line: none; cursor: pointer; font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;"><span style="color:#000000;">#信号后依次拉高SLP_S5#</span></span><span style="color:#000000;"><span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">，SLP_S4</span></span><span style="margin: 0px; padding: 0px; text-decoration-line: none; color: rgb(0, 0, 0); cursor: pointer; font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">#，SLP_S3#</span><span style="color:#000000;"><span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">信号给EC。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">EC发出PCON#给ATX电源。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">ATX电源接到低电平的PSON#信号后，开始工作，发出各路基本电压给主板上的各个元件。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">基本电压变换的其他电压也被转换出来。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">电源发出PWROK#给EC，EC转交给南桥和北桥（有的话）</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">VRM和CPU通讯，根据VID送出Vcore</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">VRM发生VRMPWRGD#给南桥，表示核心电压OK。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">南桥发送PLT_RST#给北桥。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">南桥发送PWRGOOD#给CPU。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">北桥在收到PLT_RST</span></span><span style="margin: 0px; padding: 0px; text-decoration-line: none; color: rgb(0, 0, 0); cursor: pointer; font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">#信号后，1秒钟后发生CPU_RST#</span><span style="color:#000000;"><span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">，让CPU复位</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">时序图如下：</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">青铜时代：神秘消失的时间</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">在CPU复位后，是不是要立刻跳到reset vector开始执行BIOS程序了呢？还没有，pcode、on die rom会在这个阶段执行，TXT、boot guard等安全保障措施也在这里运行。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">城邦时代：UEFI的四个阶段</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">CPU终于开始执行reset vector的代码了，这就进入了我们熟悉的UEFI的世界。我们之前已经有很多文章都有介绍UEFI的各个阶段，这里简单回顾一下：</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">在SEC阶段，系统从复位开始运行（由主机引导处理器取回的第一指令），通过初始化处理器高速缓存（Cache）来作为临时内存使用，我们有了堆栈，从而可以执行c程序，然后转到PEI阶段。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">在PEI最开始阶段，仅少量栈和堆可用，我们需要找到并使能足够我们使用的永久内存，通常是内存颗粒或内存条（DIMM），然后转入DXE。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">DXE阶段有了永久存储空间，真正开始负责初始化核心芯片，然后转换到BDS阶段。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">核心芯片初始化完成后BDS阶段开始，并继续初始化引导操作系统（输入，输出和存储设备）所需的硬件。 纵观PI的整个阶段，BDS对应的是&ldquo;执行UEFI驱动程序模型&rdquo;来引导OS这一过程。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">UEFI引导阶段步骤和驱动程序众多，经过多年发展，核心代码已经超过一百万行，俨然已经是个独立的小王国了。要理解UEFI，必须理解UEFI的目的：初始化硬件，安全启动操作系统，并为操作系统提供统一的硬件抽象。所有纷繁复杂的驱动和表象后面，都在为了这一目的服务。只要抓住这条主线，再遇到其他的知识点也就会豁然开朗了。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">近代和现代：引导程序和操作系统</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">UEFI会在BDS阶段后加载操作系统引导程序，也就是OS loader。不同的OS有不同的Loader。一般用户都十分熟悉，我们这里不再赘述。</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">另外传统BIOS和BIOS引导方式已经被淘汰。Intel也宣布对传统BIOS兼容模式（CSM）在2020后不再支持（参考资料1）。网上诸多Int3、引导扇区等内容，除非对历史有兴趣，全部可以一笑而过了。<br />
	<img alt="" src="/uploads/171127/1-1G12H1461K30.jpg" style="width: 640px; height: 473px;" /></span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">结论</span><br style="color: rgb(204, 199, 217); font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px; background-color: rgb(64, 51, 102);" />
	<span style="font-family: punctuation, PingFangSC-Regular, &quot;Microsoft Yahei&quot;, sans-serif; font-size: 15px;">按下电源键，CPU并不是第一个得到通知并立刻执行代码的。简单的开机后面隐藏了如此丰富的内容，这是很多人想象不到的。很多主板，尤其是很多服务器主板，从按下电源键到CPU开始执行UEFI固件程序，期间经历了很多隐藏的片段。这些片段可长可短，有的转瞬即逝、有的却让人等上片刻。它们究竟是什么，为什么存在，值得大家细细探究。</span></span></h3>

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